Microfluidic chips are chips having a plurality of channels. Typically the channels have a width of less than 1 mm. They are useful as ‘labs on a chip” and may be used, for example, for enzymatic analysis, DNA analysis, proteomics etc. Indeed operations such as sample preparation, pre-treatment and assay detection may be integrated onto a single chip. Chemical reactions at the small scale of the microfluidic chip tend to occur rapidly and use minimal amounts of material, thus saving time and money.
Droplet-based microfluidics has been attracting more and more interest because of its ability to perform a large number of different experiments without increasing the device size or complexity. In the form of droplets, reagents are conveyed precisely in discrete volumes, e.g. ranging from nano to pico liter size, so that high throughput chemical reaction and single cell manipulation in bio-testing can be achieved. Furthermore, by using microfluidics, mixing of reagents in droplets has been proved to be achievable in millisecond(s), thus enabling multi-step chemical reactions.
Various flow focusing, pump driven and other arrangements have been used to drive fluids and control operations on the microfluidic chip. Any pumps and valves tend to be driven by external electrical signals generated by external electronic circuitry. Digital microfluidics is the control of droplets by use of digital signals (i.e. 1 or 0).
Electrorheological (ER) fluid has been widely studied on the macroscale as a type of ‘smart’ material. An ER fluid is a fluid which transforms to solid form on application of a sufficiently strong electrical field. More recently, a new type of ER fluid was developed with giant electrorheological (GER) effect—see for example U.S. Pat. No. 6,852,251, which is incorporated herein by reference. It consists of urea-coated nanoparticles suspended in sunflower oil. Under a sufficiently strong electric field, GER fluid can transform into an anisotropic solid, with a yield stress characterizing its strength. These rheological variations can occur within 10 milliseconds and are reversible when the field is removed. The GER fluid can work as a digital fluid if a coded electrical control signal is provided to control the fluid.